Radio receiver control circuits



Nov. 12, 1940.v o. E. KEALL ET Al.

y RADIO RECEIVER CONTROL CIRCU'IS Filed Aug. l2, 1938 2 Sheets-Shea?l 1 m m s u Al WN, I l` 0..

INVENTORS OSWOLD E. KEALL M; RUST AND N05 H6 ,www

` ATTORNEY.

Nov.,12, 1940. i o. E. Kl-:ALL ET A1. 2,221,096

RADIO RECEIVER CONTROL CIRCU ITS Filed Aug. l2, 1938 2 Sheets-Sheet 2 AAAAAIA Vvvvvv Patented Nov.` 12, 1940 UNITED STATES 2,221,096 .Y RADIO' RECEIVER CONTROL cntcurrs oswola Eawaraneau mi` Nl vMem Rust, y

v Chelmsford, England, assignors to Radio Gorporation of America, a

Ware

Application August 12, 1

corporation of Dela- 938, serial No. 224,428

In Great Britain September 4, 1937 14 claims. (ci. 25o-20)A This invention relates to radio and like receivers and has for its object to provide an improved receiver the response of which is automatically controlled to an improved degree to suit the receiving conditions prevailing at any time.

It is well known automatically to control the selectivity of a radio receiver in such a way that, when receiving weak. signals the selectivity is high and, accordingly, the fidelity is somewhat low, whereas, when receiving strong signals the selectivity is reduced and the fidelity accordingly improved. In most selectivity control systems the said control is effected automatically in dependence upon the strength of the desired signals, though it may be effected in dependence upon the strength of the undesired interfering signals, or upon the relationship between strengths of the desired and interfering signals. Control systems of the nature above described are termed automatic selectivity control (ASC) systems.

It is also well known in radio and like receivers to provide means operated in dependence upon departures of a frequency actually produced. in some part of. the receiver (usually the I. F. of a superheterodyne receiver) from the frequency which should be produced there if the receiver is correctly tuned, to vary the tuning. In such control systems as at present known-these systems are termed automatic frequency control (AFC) systems-the tuning is varied to correct for such departures. v

According to this invention a radio or like receiver having an ASC system and an AFC system is characterised in that the two systems are operatively interlinked in such manner that, in the event of reception of an interfering signal, the selectivity and control is accompanied by an automatic control of tuning in a direction to tune away .from the interfering transmission. This action, of course, involves that, in the presence of interference, the tuning will not be strictly accurate but the advantages obtained far outweigh the disadvantages incident upon slight inaccuracies of tuning.

The invention is illustrated in the accompanying diagrammatic drawings wherein Fig. 1 shows a circuit embodying the invention, Fig. 2 shows a modied circuit'that can be used between points A, B, C and D of Fig. 1, and Fig. 3 shows a modification of the circuit arrangement in Fig. 1.

Referring to Figure 1 which shows diagrammatically one embodiment, I is an intermediate frequency amplier valve-as shown, a pentodeto the rst or control grid 2 of winch signals Ifromav preceding stage (not shown) are applied via the vusual tuned I. F.` input circuit 3 and ycoupling condenser 4'. The screen grid, suppressory grid and anode are represented at 5, 8 and y'I v respectively. Positive feed back is applied across .the valvey by means of a screened half wave line 8 which is in series with a condenser 9 and resistances'l, II, as shown, between a tap I2 on the tuned lanode circuit I3 of the valve and a l0 taplA on the input circuit 3. The coil I5,1cou pled tothe circuit I3, feeds into the next stage. The cathode I6 `:ofthe valve I is connected to earth through a "circuit the impedance of which produces negative -feed back effects. This cirl5 `cuit includes, inseries, a capacity shuntedresistance Il and two coils I8, I9 in series. vThe 4coils jI-8, I9 are coupled to tuned circuits 20, 2|- joneto each-which at. one end are connected to Atheanodes126y2l of a diode 25. 'I'he diode 20 cathode 124; isY connected through, a capacity shunted resistance23, and thence va capacity shunted resistances 3I, 32, to the remaining ends of the circuits 2li, 2I. The cathode 24 is connected through a resistance 29 and a grid re- 25 sistance 30 to the grid 2. 28 is a by-pass condenser. For the case of a broadcast receiver the circuits 20, 2| are tuned respectively about 9 k. c. above and 9 k. c. below the carrier-in the case of a superheterodyne receiver (the usual and 30 preferred case), the mid-band frequency of the intermediate frequency energy. 33 represents another carrier frequency valve of the receiver (operating at I. F.), the valve having in its cathl odeleg a capacity shunted bias resistance in se- 35 ries with two coils 34, 35 coupled respectively to tuned circuits 36, 3l which are preferably tuned about 1 k. c. above and below (respectively) the mid-band `frequency of the I. F. energy. The tuned circuits are connected each at one end as 40 shown to the anodes 38, 39 of a double diode 40, the remaining ends of the circuits 36, 3l being connected together through similar capacity shunted resistances 4I, 42 the point between which is connected to the cathode 43 of the 45 diode. The point D at the upper end of resistance 3l is connected to the lower end of resistance 42 while the upper end of resistance 4I is connected to a lead 44 over which automatic frequency control (AFC) bias is applied to effect 50 tuning controle. g. kthe bias 44 may be applied to the grid of an AFC valve (not shown) connected in known manner to act as a variable reactance in the frequency determining circuit of the local oscillator (not shown) of the receiver. 55

With this arrangement the bias applied through resistance 30 to the grid 2 will clearly control the selectivity of the stage of which the valve l forms part in a sense to increase said selectivitir with decrease in signal strength on grid 2 and vice versa. Furthermore, the total AFC potential on lead 44 will be made up of two components, namely (1) the usual component provided by the network of which the diode 40 forms part and (2) a superimposed asymmetrical component from the network of which the diode 25 forms part. As regards this superimposed component, if there is an interferingsignal this component will increase and modify the AFC bias on lead 44 in a sense to vary the tuning of the receiver away from the interfering transmission and thus permit the use of less selectivity-and therefore higher fidelitythan would be otherwise permissible. Looked at in another way an interfering signal, by virtue of the output from the network associated with diode 25, puts a bias on the control device which causes the circuit as a whole to adjust itself to afrequency other than fo (the I..F. mid-band frequency), the connections being so made that this frequency is on the side of fo opposite to the interfering signal.

Figure 2 shows another modified network which may be substituted for the network between A, B, C, D, in Figure 1. The main change in Figure 2 is in the provision of the further diode 46 in series with an I. F. tuned circuit 41 together in parallel across the resistance 23. Intermediate frequency energy from any convenient subsequent point in the receiver is fed to the coil 22 which is coupled to the circuit 41. With this arrangement the bias change between C and earth will depend inter alia on .the relative strengths of desired and interfering signals. Thus, whereas in Figure 1 the selectivity control is dependent-on the desired signal strength only, in Figure' 2 it is dependent on the relative strengths of desired and undesired (interfering) signals.

The invention is not limited to the precise circuits shown. For example, in Figure 3 the selectivity control is obtained by means of a meter movement comprising a coil 48 and armature l which controls, through a mechanical linkage represented at 5e, the tightness of coupling of the elements of band pass input and output -circuits 5|, 52 associated with the valve I. The winding L18 is in the anode circuit of a valve 52 having a grid the potential of which is .controlled by voltage set `up across resistance 23. The lead 53 is taken to the normally provided AVC diode (not shown) and AVC potential is applied over the lead 55. l If desired a so-called muting circuit (not shown) of any known form may be energized from the circuit 55. In other respects the circuit of Figure 3 is sumciently like that of Figure 1 to require no further description.

Having now particularly described and ascertained the nature of our said invention' and in what manner the same is to be performed, we declare that what we claim is:

1. In a modulated carrier transmis-sion system of the type provided with a carrier-tuned network, means responsive to a frequency shift of the carrier energy adapted to compensate for said shift, a second means responsive to the amplitude of carrier energy on an adjacent channel for developing control voltage from said adjacent carrier energy, and additional means for causing said compensation due to said rst means to be additionally responsive to said control voltage.

2. In a modulated carrier transmission system of the type provided with a carrier-tuned network, means responsive to a frequency shift of the carrier energy adapted to compensate for said shift, a second means responsive to the amplitude of carrier energy on an adjacent channel for developing control voltage from said adjacent carrier energy, additional means for causing said compensation due to said first means to be additionally responsive to said control voltage, and means for applying said control voltage to said carrier-tuned network to control the selectivity thereof.

3. In a modulated carrier transmission system of the type provided with a carrier-tuned network, means responsive to a frequency shift of the carrier energy adapted to compensate for said shift, a second means responsive to the amplitude of carrier energy on van adjacent channel for developing control voltage from said adjacent -carrier energy, and additional means :for causing said compensation due to said first means to be additionally responsive to said vcontrolvoltage, and ymeans responsive to said control voltage for adjusting the frequency response of said carrier-tuned network.

4. In a modulated carrier transmission system of the type provided with a carrier-tuned network, means responsive to Ya frequency .shift of the carrier energy adaptedto compensate for said shift, a, second means responsive to the amplitude of carrier energy on an adjacent channel for developing control voltage from said adjacent carrier energy, and additional means .for causing said compensation. due. to said first means to be additionally responsive .to said control voltage, said additional means -comprising connections for applying said control voltage to first responsive means.

5. In a radio receiver having acarrier-'tuned network, means responsive to a departure .of vthe carrier frequency from a predetermined frequency value for providing control voltage adapted to be used for compensating for said departure, a carrier rectifier network, responsive to energy of a carrier whose frequency yis separated from the predetermined frequency by a desired frequency value, for producing a second control voltage, and means for superimposing the second voltage on the first control voltage.A

, 6. In a radio receiver having a `carrier-tuned network, means responsive to a departure'of the `carrier frequency from a predeterminedfrequency value for providing control voltage .adapted to vloe used for compensating for said departure, a carrier rectifier network, responsive to energy of a carrier `whose frequency iszseparat'ed from the predetermined frequency by a desired frequency value, for producing a second control voltage, means for superimposing the second voltage on the first control voltage, and yrneans responsive to the second control voltage for padjusting the selectivity of the carrier-tuned `network.

7. In a radio receiver 'having a Vcarrier-tuned network, means responsive to a departure ofthe vcarrier frequency vfrom a predetermined frevquencyvalue for providing control voltage adapted to be used for compensating for' said departure, a carrier rectifier network, responsive Ito /energy .of a carrier whose frequency is separated from the `predetermined frequencyby a desired frequency value, for producinga second control voltage, means for superimposing the second voltage on the first control voltage, said carriertuned network being of the feedback type, and means responsive to the second control voltage for controlling the magnitude of feedback in said carrier-tuned network.

8. In a radio receiver having a carrier-tuned network, means responsive to a departure of the carrier frequency from a predetermined frequency value for providing control voltage adapted to be used for compensating for said departure, a carrier rectifier network, responsive to energy of a carrier whose frequency is separated from the predetermined frequency by a desired frequency value, for producing a second control voltage, means for superimposing the second voltage on theiirst control voltage, and means responsive -to said rectifier network for adjusting the selectivity of said carrier-tuned network in the same sense as the amplitude of the separated carrier.

9. In a radio receiver having a carrier-tuned network, means responsive to a departure of the carrier frequency from a predetermined frequency value for providing control voltage adapted to be used for compensating for said departure, a carrier rectifier network, responsive to energy of a carrier whose frequency is separated from the predetermined frequency by a desired frequency value, for producing a second control voltage, means forr Superimposing the second voltage on the first control voltage, means responsive to said rectifier network for adjusting the selectivity of said 'carriertuned network in the same sense as the amplitude of the separated carrier, and additional means responsive to the amplitude variation of the carrier of predetermined frequency for controlling the transmission efiiciency through said receiver.

10. In a superheterodyne receiver provided with an intermediate frequency amplifier having at least one resonant network tuned to a desired operating frequency value, means for adjusting the selectivity of said resonant network, a discriminator, responsive to a frequency shift of the the selectivity of said resonant network, a discriminator, responsive to a frequency shift o-f the intermediate frequency energy from said operating value, for providing a shift-compensation voltage, a second discriminator, responsive to carrier energy spaced from said frequency value by a predetermined frequency magnitude, for providing a pair of voltages of opposite polarity, means for supermposing one of the pairl of voltages on said compensating voltage, and means for controlling said selectivity adjusting means ywith the second of said pair of voltages.

12. In a superheterodyne receiver provided with an intermediate frequency amplifier having at least one resonant network tuned to a desired operating frequency value, means for adjusting the selectivity of said resonant network, a discriminator, responsive to a frequency shift of the intermediate frequency energy from said operating value, for providing a shift-compensation voltage, a second discriminator, responsive to carrier energy spaced from said frequency value by a predetermined frequency magnitude, for providing a pair of voltages of opposite polarity, means for superimposing one of the pair of voltages on said compensation voltage, and

means for coupling the second discriminator to the'said amplifier.

13.` In a superheterodyne receiver provided with an intermediate frequency amplifier having at least one resonant network tuned to a desired operating frequency value, means for adjusting the -selectivity of said resonant network, a discriminator, responsive to a frequency shift of the intermediate frequency energy from said operating value, for providing a shift-compensation voltage, a second discriminator, responsive to carrier energy spaced from said frequency value by a predetermined frequency magnitude, for providing a pair of voltages of opposite polarity, means forr superimposing one of the pair of voltages on said compensation voltage, said first discriminator comp-rising a pair of rectifiers coupled to said amplifier, and said second discriminator comprising a pair of rectiiiers coupled to said amplier.

14. In a superheterodyne receiver provided with an intermediate frequency amplifier having at least one resonant network tuned to a desired operating frequency value, means for adjusting the selectivity of said resonant network, a discriminator, responsive to a frequency shift of the intermediate frequency energy from said operating value, for providing a shift-compensation voltage, a second discriminator, responsive to carrier energy spaced from said frequency value by a predetermined frequency magnitude, for providing a pair of voltages of opposite polarity, and means for superimposing one of the pair of voltages on said compensation voltage, said amplifier having a feedback circuit comprising said selectivity adjusting means. j

OSWOLD EDWARD KEALL. Noi; MEYER RUsT. 

